Compositions for producing glass coatings by way of inkjet printing techniques and use thereof

ABSTRACT

A coating material for the production of a UV-curing primer coating. The coating material includes at least 60 to 90 wt.-% of at least one monofunctional cycloaliphatic acrylate monomer or at least one monofunctional aryloxy alkyl acrylate monomer, 1 to 10 wt.-% of at least one amino-functional silane, 1 to 10 wt.-% of at least one photoinitiator, and up to 10 wt.-% of at least one of at least one acrylate oligomer and at least one methacrylate oligomer, each based on a total weight of the coating material.

The present invention relates to coating materials and their use for the production of coatings and coating systems for glass surfaces. Furthermore, the invention relates to digital methods for printing on glass substrates, in particular flat glass and glass-formed containers.

Digital printing methods or digital printing is/are defined as printing methods whose print image is directly transmitted from a computer to a printing unit without any use of a static printing form. Known digital printing methods are electrophotographic printing methods and inkjet printing methods.

For the decoration of glass surfaces inkjet printing methods are usually used. Up to now, the required durability of the decoration of, for instance, drinking glasses, beverage bottles and other glass packagings can only be obtained by complex multilayered coating systems, with the glass surfaces being pre-treated by means of flame-pyrolytic surface silicating technology in a first step. Afterwards, a primer layer is applied, with the primer coating material or the primer coating materials being applied to the pre-treated glass surface either by way of dipping, spraying, rolling or wiping. Alternatively, common printing methods like, for instance, serigraphy are also employed.

The term “primer layer” or “primer coating” is defined hereafter as the first layer of a coating system that is applied to a substrate. The primer layer may consist of at least one coating, which is produced from at least one coating material.

The decorative layer containing at least one ink coating that has been produced from inks by means of inkjet printing methods, is applied to the primer layer. Finally, a top coat layer consisting of at least one top coat is applied to the decorative layer. The top coats can be applied by means of inkjet printing methods or common printing or coating methods. The term “top coat” is defined hereafter as the topmost layer of a coating system, which protects the subjacent layers from mechanical damage and chemical stress.

A disadvantage of the printing used to date is the employment of different application, curing and printing methods that require a lot of work and time. Furthermore, the costumarily employed primer coating materials show a solvent content of more than 90% by weight. Hence, after the application of the coating materials some time is required for the solvent to evaporate out of the applied layer. In addition to this, higher amounts of solvent vapours are produced which have to be conducted away in a complex manner. A further disadvantage is that usual primer coating materials cannot automatically be applied by means of inkjet printing techniqes in a reliable way. That means that a further application technology has to be integrated in the printing unit.

Patent application US 2012/0077896 A1 discloses radiation-curable inkjet inks, which have a good adhesiveness to glass surfaces. By curing they become alcohol- and water-resistant coatings, which do not require any further primer coatings or top coats. However, coatings thus obtained are not sufficiently scratch- and water-resistant and they are dishwasher safe only to a small extent.

Hence, the problem of the present invention is to provide improved coating systems for the decoration of glass bodies by means of inkjet printing methods, as well as improved methods for printing on glass surfaces. The problem is solved by coating materials according to the first claim as well as coating systems and methods for the production thereof according to the independent claim. Further embodiments are disclosed in the dependent claims and the description.

Decorations printed on glass surfaces, especially decorations on articles of daily use like, for instance, beverage bottles and drinking glasses, have to be scratch- and water-resistant and dishwasher safe. It has turned out that the radiation-curable primer coatings according to the invention reveal a strong anchoring between the glass surface and the coating system. In particular, adhesiveness and durability of the decoration coatings printed by means of inkjet printing methods are improved significantly.

According to the invention, the primer coatings are produced from coating materials comprising at least 60 to 90% by weight of monofunctional cycloaliphatic acrylate monomers or monofunctional aryloxy alkyl acrylate monomers, 1 to 10% by weight of amino-functional silanes, 1 to 10% by weight of photoinitiators, up to 10% by weight of acrylate oligomers and/or methacrylate oligomers as well as up to 1% by weight of surfactants, each based on the total weight of the coating material. Preferred acrylate monomers are phenoxyethyl acrylates and/or trimethylol-propane formal acrylates. According to the invention, the monofunctional acrylate monomers are preferably employed in quantities of 70 to 90% by weight, more preferably 80 to 90% by weight, each based on the total weight of the coating material.

Preferred amino-functional silanes are bis[(3-trimethoxysilyl)propyl]amine and aminopropyltriethoxysilane. According to the invention, the silanes are preferably employed in quantities of 1 to 8% by weight, more preferably 2 to 7% by weight, each based on the total weight of the coating material.

Suitable photoinitiators are phosphine oxide derivatives. Preferred photoinitiators are bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. According to the invention, the photoinitiators are preferably employed in quantities of 2 to 9% by weight, based on the total weight of the coating material.

Suitable acrylate oligomers and methacrylate oligomers are polyester acrylate oligomers, polyester methacrylate oligomers, polyether acrylate oligomers, polyether methacrylate oligomers, urethane acrylate oligomers and urethane methacrylate oligomers. Preferred oligomers are polyester acrylate oligomers and urethane methacrylate oligomers. According to the invention, the acrylate oligomers and/or methacrylate oligomers are preferably employed in quantities of 0.01 to 10% by weight, more preferably 1 to 10% by weight, most preferably 1 to 8% by weight, each based on the total weight of the coating material.

Suitable surfactants are modified poly(organo)siloxanes. Preferred surfactants are silicone polyether derivatives. According to the invention, the surfactants are preferably employed in quantities of 0.01 to 1% by weight, based on the total weight of the coating material. In addition, the primer coating materials may contain further auxiliary agents and additives known to and commonly used by a skilled person, like, for instance, polymerization inhibitors or defoamers.

The primer coatings according to the invention are cured by radiation in a wavelength range of between 450 and 180 nm. The employed radiation may be generated, for example, by means of ultraviolet light emitting diodes (LED) or mercury vapour lamps. Therefore, LED spots, for example, with a power of 10 to 20 W or medium pressure mercury lamps with a power of 200 to 500 W/cm can be employed.

In one embodiment the coatings obtained from the coating materials according to the invention are employed as primer layers on glass surfaces. They are particularly employed as primer layers in coating systems for the decoration of glass surfaces on which inkjet methods effect printing.

A further embodiment of the present invention discloses a coating system for the decoration of a glass surface comprising a primer layer produced from at least one primer coating, a decorative layer produced from at least one ink layer, and a top coat layer produced from at least one top coat.

The primer coatings are produced from UV-curing coating materials containing at least 60 to 90% by weight of monofunctional cycloaliphatic acrylate monomers or monofunctional aryloxy alkyl acrylate monomers, 1 to 10% by weight of amino-functional silanes, 1 to 10% by weight of photoinitiators. In addition, the primer coating materials may contain up to 10% by weight of acrylate oligomers and/or methacrylate oligomers as well as up to 1% by weight of surfactants.

For the production of the coatings of the decorative layer UV-curing inks are employed, which are suitable for inkjet printing method. The inkjet inks preferably contain pigments, oligomers, photoinitiators and reactive diluents. They can also contain further additives known to and commonly used by a skilled person.

In a first step, in order to improve the print image, light, preferably white ink coatings may be applied to the primer layer. These coatings are produced from inkjet inks that preferably contain white pigments. Afterwards, the colour inks are applied to the white ink coatings. For this purpose those inks are employed, which contain the usual colours for colour printing.

For the production of the top coat layer transparent coatings are preferably employed, which are produced from UV-curing clear coats. The term “clear coat” is defined hereafter as a coating material providing a transparent coating, which may also have decorative and technical effects besides the protective properties. Suitable clear coats according to the invention are oligomers, reactive diluents and photoinitiators and, if need be, further additives known to and commonly used by a skilled person.

The coating system according to the invention leads to particularly durable print images, which correspond in particular to the requirements on decorations of food containers like beverage bottles and drinking glasses. They show a high scratch and water resistance and are highly dishwasher safe.

A further embodiment of the present invention discloses a method for printing on glass surfaces, which shows the following steps:

-   -   (a) Applying at least one primer coating material by means of         inkjet printing methods,     -   (b) pre-gelling of the applied coating material or the applied         primer coating materials by UV radiation,     -   (c) applying at least one ink by means of inkjet printing         methods,     -   (d) pre-gelling of the applied ink or the applied inks by UV         radiation,     -   (e) applying at least one clear coat by means of inkjet printing         methods,     -   (f) curing of the entire layer construction by UV radiation.

For the pre-gelling or pinning in steps (b) and (d) LED spots emitting radiation with a wavelength of 385 or 395 nm are preferably used as radiation source. Power lies between 2 and 5 W. Radiation is preferably effected with a dose in the range of between 20 and 100 mJ/cm².

In the last step (f) the entire layer construction, which comprises a primer layer consisting of the pre-gelled primer coatings, a decorative layer consisting of the pre-gelled ink coatings and a top coat layer consisting of the pre-gelled clear coats, is completely cured by radiation with rays or light in a wavelength range of between 450 and 180 nm. For this purpose medium pressure mercury lamps are preferably employed, which have a power of 200 to 500 W/cm and a preferred dose of 500 to 2000 mJ/cm².

In a preferred embodiment of the method, steps (c) and (d) are executed by use of white inks in a first step, then they are repeated using colour inks. In doing so, light, preferably white ink coatings are generated, on which the actual image or decoration is printed. A significantly improved print image is obtained thanks to the white ground, especially on colour or dark substrate surfaces.

The UV-curing primer coating materials, inks and clear coats are applied by means of commercially available inkjet printers. Inkjet printers that are suitable for printing on moulded objects are preferably employed. The printed coating materials are pre-gelled or exposed to pinning. The terms “pre-gelling” and “pinning” are defined hereafter as the fixation of a coating material through pre-reaction. The coating material is pre-gelled, this means that it is pre-cured to an extent that it is not liquid any more. It already develops a sufficiently hard coating, which, however, is not yet completely cured. This method avoids undesirable running and improves adhesion of the coating materials.

In the last step the entire layer construction consisting of primer layer, decorative layer and top coat layer is completely cured. During this final curing of all imprinted and pre-gelled layers the coatings cross-link, so that very stable layer constructions are generated. In order to improve chemical and mechanical bonding of the primer layer, in a further embodiment of the present invention the glass surface may be pre-treated by flame-pyrolytic surface silicating prior to printing. In this process the oxidative reaction of organic silicon compounds like, for instance, silanes leads to a solid nanoporous silicate layer, which partially hydrolyzes. Thus, reactive hydroxyl groups are created and the surface energy increases.

The method according to the invention can be executed with a chart speed of 5 to 20 m/minute, which is common for production lines. It can therefore easily be integrated as in-line method for the decoration of glass. As primer coating materials as well as inks and clear coats are applied by means of inkjet printing methods, it is possible to employ only one print module for these in-line methods.

The method according to the invention is suitable for printing on flat glass and glass-formed containers, in particular for printing on drinking glasses, beverage bottles and glass packagings for food.

EXAMPLE Example 1

Composition of the primer coating material

Quantity Constituent [% by weight] Phenoxyethyl acrylate 83.5 Urethane methacrylate oligomer 5.0 Bis[(3-trimethoxysilyl)propyl]amine 5.0 Silicone polyether acrylate 0.5 Bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide 3.0 2,4,6-trimethylbenzoyl-diphenylphosphine oxide 3.0

Printing Method:

A commercially available inkjet printing plant for rotationally symmetric bodies with a print head type Konica Minolta KM1024 was used for printing. Printing was executed on commercially available drinking glasses. In a first step, the glass surfaces were pre-treated by flame-pyrolytic surface silicating. Afterwards the primer coating material according to example 1 was imprinted with a resolution of 360×360 dpi with a printing speed of 20 m/min. Then a pinning of the imprinted coatings by an LED spot with a power of 2 W at a wavelength of 395 nm was effected. On the pre-gelled primer coating, a commercially available white UV-curing inkjet ink was imprinted with a resolution of 360×360 dpi and a printing speed of 20 m/min. Then a pinning of the imprinted coating was effected by an LED spot with a power of 2 W at a wavelength of 395 nm. Commercially available UV-curing inkjet colour inks were printed on the pre-gelled white ink coating with a resolution of 360×360 dpi and a printing speed of 20 m/min. Then a pinning of the imprinted coating by an LED spot with a power of 2 W at a wavelength of 395 nm was effected. A commercially available UV-curing clear coat that is suitable for inkjet printers was printed on the pre-gelled colour ink coatings with a resolution of 360×360 dpi and a printing speed of 20 m/min. Then all imprinted and pre-gelled coatings were cured by radiation by means of a medium-pressure mercury lamp with a power of 270 W/cm.

Determination of Scratch Resistance:

A weight-loaded scratch stylus (model Erichsen 435S) was placed with its tip on the coating to be tested and was then, vertically upright, pulled over the surface to be tested. Then it was visually assessed whether the tested coating had a scratching track. The maximum mass of weight with which the scratch stylus can be loaded without the coating being damaged during the test is a measure of the scratch resistance of the coating. A result of more than 5 newtons or more without damage on the coating is considered as being a good scratch resistance.

Determination of Adhesion (Cross-Cut Test):

For a cross-cut, six parallel cuts are applied to the coating of the test specimens with a cutter knife. The cuts in the coating are so deep that they reach the substrate surface without damaging it. Then further six parallel cuts are applied which are perpendicular to the first ones and form an even square or lattice. The grid spacing is 1 mm. A clear or crepe tape strip with an adhesive force of 8 to 10 N/25 mm is sticked onto the resulting square. It is removed at an angle of 60% in a time of 0.5 to 1 s. Then the grid or coating is assessed visually. The grid cut characteristic value Gt 0 corresponds to a very good adhesive strength, and the characteristic value Gt 5 corresponds to a very poor adhesive strength.

Determination of Adhesion (Tape Test)

On the coated specimen, an adhesive tape strip (type Tesa-Film 57370-00002) is fixed on the coating to be tested using light pressure and avoiding inclusions of air. After having waited for 10 seconds, the adhesive tape strip is removed in an angle of 60° and visually assessed. The result is considered to be good if no residues can be seen on the adhesive tape strip.

Determination of Water Resistance:

The specimen is completely immersed into water for 3 days at a temperature of 23° C. Then the specimen is removed from water and without reconditioning its adhesion (cross-cut test and tape test) and scratch resistance are checked. Water resistance is considered to be good, if the three tests after immersion of the specimens into water do not provide worse results than prior to the immersion into water.

Determination of the Specimens with Regard to the Question Whether they are Dishwasher Proof:

The specimen is washed in a commercially available industrial dishwasher with a commercially available industrial dishwashing liquid for 10 minutes at a temperature of 60 to 75° C. Afterwards, the coating surface is visually assessed, with the surface being particularly evaluated with respect to changes in surface and colour. After a 10-minute reconditioning at 23° and at 50% relative humidity of air the cross-cut test and tape test are executed. Then the quantity of wash cycles without worsening of the test results is determined.

The test results are summarized in the following table.

Table: Summary of Results

Result Result Result after after directly immersion 1000 after into wash Test curing water cycles Scratch resistance >5N >5N >5N Cross-cut test GT 0 GT 0 GT 0 Tape test no residue no residue no residue Visual assessment Reference no change no change

All specimens show a good adhesion of the coating to the substrate as well as a high scratch resistance, which do not worsen either after cleaning processes. The influence of water, chemicals and temperature as it occurs with usual cleaning methods do not reveal any recognizable effect on the glass coating. 

1-15. (canceled)
 16. A coating material for the production of a UV-curing primer coating, the coating material comprising: at least 60 to 90 wt.-% of at least one monofunctional cycloaliphatic acrylate monomer or at least one monofunctional aryloxy alkyl acrylate monomer; 1 to 10 wt.-% of at least one amino-functional silane; 1 to 10 wt.-% of at least one photoinitiator; and up to 10 wt.-% of at least one of at least one acrylate oligomer and at least one methacrylate oligomer, each based on a total weight of the coating material.
 17. The coating material as recited in claim 16, further comprising: up to 1 wt.-% of at least one surfactant based on the total weight of the coating material.
 18. The coating material as recited in claim 17, wherein the at least one surfactant is a modified poly(organo)siloxane.
 19. The coating material as recited in claim 16, wherein the at least one monofunctional cycloaliphatic acrylate monomer is at least one of phenoxyethyl acrylate and trimethylol-propane formal acrylate.
 20. The coating material as recited in claim 16, wherein the at least one amino-functional silane is at least one of bis[(3-trimethoxysilyl)propyl]amine and aminopropyltriethoxysilane.
 21. The coating material as recited in claim 16, wherein the at least one photoinitiator is a phosphine oxide derivative.
 22. The coating material as recited in claim 16, wherein the coating material comprises 0.01 to 10 wt.-% of at least one of the at least one acrylate oligomer and the at least one methacrylate oligomer, each based on the total weight of the coating material.
 23. The coating material as recited in claim 16, wherein the at least one acrylate oligomer and the at least one methacrylate oligomer is selected from the group consisting of a polyester acrylate oligomer, a polyester methacrylate oligomer, a polyether acrylate oligomer, a polyether methacrylate oligomer, a urethane acrylate oligomer, a urethane methacrylate oligomer, and mixtures thereof.
 24. A coating system for the decoration of a glass surface, the coating system comprising: a primer layer comprising at least one primer coating, the at least one primer coating being produced from the coating material as recited in claim 16; a decorative layer comprising at least one ink coating; and a top coat layer comprising at least one top coat.
 25. The coating system as recited in claim 24, wherein the at least one ink coating is produced via at least one UV-curing inkjet ink.
 26. The coating system as recited in claim 24, wherein the at least one top coat is produced from a UV-curing clear coat.
 27. A method for printing on a glass surface, the method comprising the steps of: (a) applying to the glass surface the at least coating material as recited in claim 16 via an inkjet printing method; (b) pre-gelling of the at least one coating material applied via UV radiation; (c) applying at least one ink via the inkjet printing method to the pre-gelled at least one coating material; (d) pre-gelling of the at least one ink applied via UV radiation; (e) applying at least one clear coat via the inkjet printing method to the pre-gelled at least one ink, to thereby obtain a layer construction; and (f) curing the layer construction via UV radiation.
 28. The method as recited in claim 27, further comprising repeating the steps of: (c) applying at least one ink via the inkjet printing method to the pre-gelled at least one coating material; and (d) pre-gelling of the at least one ink applied via UV radiation, as, (c1) applying at least one white ink via the inkjet printing method to the pre-gelled at least one coating material; (d1) pre-gelling of the at least one white ink applied via UV radiation; (c2) applying at least one color ink via the inkjet printing method to the pre-gelled at least one white ink; and (d2) pre-gelling of the at least one color ink applied via UV radiation.
 29. A method of using the method as recited in claim 27 to print on at least one of a flat glass and a glass-formed container, the method comprising: providing at least one of the flat glass and the glass-formed container; and printing on at least one of the glass surface and the glass-formed container via the method as recited in claim
 27. 30. The method of using as recited in claim 29, wherein the at least one of the flat glass and the glass-formed container includes a drinking glass, a beverage bottle, and a glass packaging for food. 